<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>边框案例</title>
		<style>
			div#cirle{
				width: 400px;
				height: 400px;
			}
			
			div#triangle{
				width: 0;
				border-left: 50px solid red;
				border-right: 50px solid yellow;
				border-bottom: 50px solid black;
			}
		</style>
	</head>
	<body>
		<div></div>
		<div id="cirle"></div>
		<div id="triangle"></div>
	</body>
</html>